The method of preparation of estrogen analogs labeled with 125I with the specific actvity of up to 2200 Ci/mmole were developed. Samples of (125i)-6-iodoestra-1,3,5,(10),6-tetraen-3,17beta-diol, specific activity 2200 Ci/mmole and 250 Ci/mmole, were prepared and used. Additional novel estrogen analogs were prepared for biological evaluation.